Multilayer optical films can incorporate a large number of thin layers of different light transmissive materials, the layers being referred to as microlayers because they are thin enough so that the reflection and transmission characteristics of the optical film are determined in large part by constructive and destructive interference of light reflected from the layer interfaces. Depending on the amount of birefringence (if any) exhibited by the individual microlayers, and the relative refractive index differences for adjacent microlayers, and also on other design characteristics, the multilayer optical films can be made to have reflection and transmission properties that may be characterized as a reflective polarizer in some cases, and as a mirror in other cases, for example.
Window films may reflect a portion of infrared and visible light and may incorporate dyes into a polymer film or may utilize metalized films. Such films absorb heat and can cause excessive heat buildup on a glass pane to the point that the glass cracks due to non-uniform thermal expansion. In addition, metalized films can undesirably block cell phone signals. There is a need for improved window film.